Edward Williams first noticed a rash on his groin and legs after playing golf one day in the rain. He thought he might have been exposed to poison ivy or had an allergic reaction to chemicals on the wet grass. But he never suspected it was a sign of a rare pancreatic cancer.

The blistering sores spread to his arms, legs and even his eyes. The Waterport, N.Y., software developer went from doctor to doctor, trying every treatment from light therapy to topical ointments to oral steroids.

Nothing worked.

"I had to hide it with long sleeves because I'm a business person," said Williams, who is now 54. "It was all over my face. I could literally shave only every other day, because it was so painful over the top of the blisters."

Williams lived with the debilitating rash for six years until a suspicious dermatologist from University of Rochester Medical Center in New York followed a hunch and diagnosed necrotic migratory erythema (NME).

Today, two years after surgery to remove the tumor on his pancreas, Williams is cancer-free.

"I feel like a new person," he told ABCNews.com. "I just thought I had a rash and was getting older and didn't have quite the energy and stamina. I truly feel like a new person. And I am taking no medicine for absolutely anything."

And nearly as important, he is rash-free. "I am back to my baby skin," he said. "I feel very fortunate."

Pancreatic cancer is almost always fatal. But Williams had a glucagonoma, a rare, slow-growing tumor of the pancreas that results in extreme overproduction of the blood-glucose-raising hormone glucagon.

His doctors say that this serious condition can often be overlooked, and Williams' story is an example of how dermatologic conditions can be a "window" to the body, revealing more serious disorders.

"The skin has an amazing ability to tell the story of a person," said Dr. Brian Poligone, 40, an assistant professor at Rochester and an attending physician at its James P. Wilmot Cancer Center, who treated Williams.

"I know if they like the sun, or if they smoke, if they are scarred from war, if they are jaundiced with alcoholism -- or what color they painted their porch last weekend," he said. "It can give you a glimpse inside sometimes even telling you that they have cancer, before they know it."

For example, blistering in the mouth -- paraneoplastic pemphigus -- can be a sign of leukemia. Scientists call these paraneoplastic conditions when a symptom is caused by the presence of cancer in the body, like hormone secretions or an immune response, but not due to the physical presence of a tumor.

In NME, the cancerous pancreas produces glucagon, which triggers a classic skin rash. Usually, though not in Williams' case, there is also diabetes, diarrhea and anemia. Weight loss is also common and Williams did, in fact, drop 30 pounds.

Williams' ordeal began six years before his diagnosis. After seeing his general practitioner about the rash, Williams was sent to a dermatologist. The doctor prescribed topical treatments but the rash persisted for months.

He was referred to another dermatologist, who ordered light treatments three times a week. Eventually, on oral steroids, he saw some relief, but the rash tended to come back in predictable cycles.

Williams would anticipate an outbreak, which happened about every four weeks. He said he would plan his business trips, interacting with clients, around the times when his skin had cleared. Other times, he would avoid the public altogether.

"It got to the point where I knew it was systemic … my body was constantly fighting this," said Williams. "When it was under my arm, it was under both arms. It was coming out on the back of my legs in the same place."

"Sometimes it would come out through my eyes and crust over, and I would have to use a warm wash cloth to get my eyes open," he said. "It was very painful on my back and the back of my shoulders."

Williams arrived in Poligone's office with a "six-inch thick" folder of medical reports from visits to other doctors.

Pancreatic Cancer Is Nearly Always Fatal

Edward Williams has this blistering rash for six years before he was diagnosed with a rare form of pancreatic cancer.

Williams didn't display any of the other "classic" symptoms of NME, which made it harder to immediately diagnose, according to Poligone.

"There were some clues, but in the end, things threw you off," said Poligone.

A poison ivy rash can also be present in the groin area, but it disappears with time.

"He had this red rash on his face and around his eyebrows and mouth and legs -- sort of one or two centimeters, red-orange plaques," he said. "At first, you consider a few things, but you don't want to do a lot of testing. As time goes on, the good doctor has to expand that differentiation and starting thinking zebra instead of horse."

Poligone knew "something was missing" and wondered if Williams could have NME because of the rash in the groin area, a telltale sign.

"It's the only case I had ever seen, though I had read about it in the textbooks," he said.

He consulted a mentor, Dr. Peter Heald, professor emeritus of dermatology at Yale, who suggested his former student was on the right track.

Poligone ordered a glucagon test and an insulin test. Both came back abnormal. He ordered a CT scan to look at Williams' pancreas, which pinpointed a tumor.

When Williams was finally diagnosed in December 2010, he Googled pancreatic tumor. "The stories weren't good. None of them had good outcomes."

With a wife and two adult daughters, aged 28 and 30, he said he thought, "O.K. How many months do I have to live? It was tough, especially during the holiday season."

Dr. Luke Schoeniger, an associate professor of surgery and oncology at Rochester, performed the operation to remove the tumor. Follow-up CT scans have shown no recurrence of the cancer.

Most pancreatic cancers carry a death sentence because they are usually so advanced before they are detected, according to Poligone.

It took six weeks to recover from surgery, but Williams began taking short walks and feeling better.

"Now when I get up in the morning, I appreciate I don't have the rash," he said. Nor the cancer, thanks to his diligent dermatologist.

"Dr. Poligone's persistence to solve my case saved my life," said Williams, who has been lucky enough to see his daughter Rebecca get married this year and give him a grandson.

His doctor is thrilled with the outcome of Williams' mystery rash.

"This is the reason we all want to go to medical school -- to get to do this," said Poligone. "It's really a great feeling to have done some good."